Known in the art are processes for producing phenol-aldehyde foamed plastics using acid agents as catalysts, which are products of condensation of sulphonated phenol with nitrogen-containing organic compounds of an amine, and amide class, and with formaldehyde in the form of an aqueous solution.
The acid agent is produced by a process comprising reacting sulphuric acid, phenol, a nitrogen-containing compound and an aldehyde in a batch reactor in three stages. In the first stage, phenol is reacted with sulphuric acid at 100.degree.-110.degree. C. for 2-24 hours. In the second stage sulphonated phenol is reacted with a nitrogen-containing compound at 40.degree.-70.degree. C. for 0.5-1 hour. In the third stage, the resultant product is reacted with an aldehyde at 40.degree.-70.degree. C. for 1-2 hours.
This process is deficient in its intermittent performance, long duration of production cycle and considerable labor and power consumption.
Nitrogen-containing compounds in the composition of the acid agent reduce corrosive activity of cured phenol-aldehyde resins and function as acceptors of formaldehyde released during the curing of phenol-formaldehyde resins.
The acid agents of this type are deficient in that phenol-aldehyde resins cured by using them are low in strength and brittle.
Known in the art is a process for producing an acid agent in which a batch reactor in two stages: in the first stage, phenol is reacted with sulphuric acid at 120.degree.-150.degree. C. for 0.5-1 hour; in the second stage, the product resulting from the first stage is reacted with formaldehyde at 30.degree.-50.degree. C. for 1-2 hours.
This process is deficient in its intermittent performance and considerable power consumption necessary to effect intense stirring of large volumes.
The acid agent produced by that process is a weak acceptor of formaldehyde released during the curing of phenol-formaldehyde resorcinols and imparts an elevated corrosive activity thereto.
It is also known to produce an acid agent by condensing phenol with an aldehyde at 95.degree.-100.degree. C. for several hours, with subsequent sulphonation of the resultant novolac with sulphuric acid at 100.degree.-120.degree. C. for 2-6 hours.
This process is deficient in that it is intermittent, has a long production cycle and requires much labor and power.
The disadvantages of such acid agents include high viscosity of sulphonated novolac, the presence of free sulphuric acid therein, sometimes in great quantities, and low content of phenolic nuclei unsubstituted with a sulphogroup, which would function as active acceptor of formaldehyde. To lower the viscosity, such acid agent is to be diluted with water thus increasing its corrosive activity.
Therefore, the following disadvantages are inherent in all known acid agents used as catalysts for curing phenol-formaldehyde resorcinols:
1. Restricted opportunity of imparting useful properties to cured phenol-formaldehyde resins.
2. High viscosity.
3. Elevated corrosive activity.
4. Reduced catalytic activity.
Known in the art is an acid agent comprising a combined aryl sulphonic acid and phenol-aldehyde novolac which is obtained by reacting an aryl sulphonic acid and oxy-(R)-methyl derivative of phenol. The following disadvantages are inherent in this process: long production cycle, the need to use cumbersome reactors for conducting the process, which should be manufactured of acid resistant materials, considerable power and labor consumption.